Brush making

ABSTRACT

A process for forming a grooming implement is provided. The steps include providing a blank having a head and a handle, wherein the head has one or more void spaces which divide said head into at least two segments, and injecting an elastomer into the void space at a temperature of at least about 245° C. thereby fusing the elastomer to the segments and forming a resiliently flexible joint. The elastomer is the sole mechanical link between the segments such that the segments can flex relative to each other and the elastomer can be stretched to about 120% of its unstressed length without separation of the elastomer from the segments.

FIELD OF THE INVENTION

The present invention relates to a process for making two component,injection moulded personal grooming implements, especially toothbrushes.In particular it relates to a process for improving the adhesion betweenthermoplastics and thermoplastic elastomers so that flexible jointsbetween the materials in the neck or head of the implement can withstandrepeated flexing without loss of adhesion at the joint. The inventionfurther relates to two component, injection moulded personal groomingimplements having high levels of adhesion between the components.

BACKGROUND OF THE INVENTION

The configuration of human teeth requires that the ideal bristle contourfor toothbrushes for brushing the buccal or outside surfaces of teeth beconcave and that the ideal bristle contour for brushing the lingual orinside surfaces of teeth be convex. Yet, most brushes are still ofrelatively rigid, single piece construction and of fixed configuration.The bodies of toothbrushes and similar implements are typically madefrom polypropylene or similar thermoplastic materials.

In many brushes a second, elastomeric component, such as a thermoplasticelastomer, is employed in the handle to aid grip or to provide adistinctive appearance. The two component brush is typically now made byinjection moulding, such as described in “Zahoransky's fully automatictwo-colour mould”. Brossa Press (1989). The process typically involves afirst moulding step in which a thermoplastic body is made, incorporatingvoids to accept the elastomer. In a second step, the elastomer isinjected into the voids where it will typically become partiallymechanically anchored, on cooling and setting, and also fused to thethermoplastic body. In the handle, the demands on the joint between thethermoplastic body and the elastomer are, typically, not high.

Brushes have, however, been described that incorporate a link forallowing the head to flex relative to the handle, as described forexample in EP-A-371,293 to EP-A-613,636. In the brushes describedtherein the flexible linking employs an elastomer to aid or modifyflexibility and the joint between the elastomer and the body will besubject to greater stress.

WO 92/17092, WO 92/17093 and WO 96/02165 disclose toothbrushes havingresiliently flexible, bristle-bearing heads, the heads, in certainembodiments being in the form of two or more segments which are flexiblyand resiliently linked to each. Gaps between the segments can be whollyor partially filled with an elastomer. In brushes of the type ofconstruction the bond between the elastomer and the body can be subjectto great stress, repeatedly applied through frequent use. However, noneof the aforementioned documents describes how to achieve a robust jointbetween the two materials which will stand up to repeated use.

It has now surprisingly been found that the strength of fusion betweenthe elastomer and the brush body can be substantially improved byraising the elastomer injection temperature above the range from 190°C.-210° C. customarily employed, without thermal degradation of theelastomer.

It is accordingly an object of this invention to provide a process formaking two component, injection moulded personal grooming implementswhich can flex resiliently and which had good long-term durability.

It is a further object of this invention to provide a two component,injection moulded personal grooming implement having increased strengthof fusion between a plastic body and an elastomer.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided aprocess for forming a resiliently flexible joint in the handle or headof a personal grooming implement; the implement comprising a handlehaving two ends, and at one end thereof, a head comprising a groomingmeans; the process comprising the steps of:

i) providing an implement blank including at least one region of plasticmaterial defining a void space in the head or the handle; and

ii) injecting an elastomer into the void space at a temperature of atleast 245° C. thereby fusing the elastomer to the plastic material andforming the resiliently flexible joint.

According to a second aspect of the invention there is provided apersonal grooming implement having an elongated handle and a headdisposed at one end thereof, the head comprising a grooming means; thehandle or head including a resiliently flexible joint between a firstregion made from a plastic material with a Vicat softening point of lessthan 245° C., and a second region made from an elastomer, wherein theelastomer is fused to the plastic material such that the elastomer canbe stretched to 120% of its unstressed length without separation of theelastomer from the plastic material.

The process of this invention provides improved adhesion between theelastomer and the plastic components so that flexible joints where thetwo components are bonded together by fusion are better able towithstand repeated flexing without degradation of the bond. Thedurability of the implement is thereby improved.

DETAILED DESCRIPTION OF THE INVENTION

The personal grooming implement of this invention can be any implementof the type that has a sufficiently elongated handle for the user togrip and, disposed at one end of the handle, a head comprising agrooming means. The implement can, for example be a toothbrush,hairbrush or a massaging implement. More especially, it is a toothbrush.

The head comprises a grooming means. The grooming means can take theform of bristles, combing teeth, polishing materials, rubber massagepads and the like. In preferred embodiments herein the implement is atoothbrush wherein the grooming means comprises a plurality of bristlesextending from the head.

The head can be detachably connected to the handle, for example topermit replacement of the head when bristles become worn, in which casethe head has a point of attachment for the handle. The head can comprisea multiplicity of connected segments. A first head segment can becontinuous with the handle. In a preferred embodiment the handle andfirst head segment is a single piece formed by injection moulding.Preferably, the handle and all of the head segments are formed within asingle mould by injection moulding. In any case the handle has alongitudinal axis extending between its two ends. This axis also definesthe longitudinal axis of the head which is co-extensive with the axis ofthe handle. Preferably the head is of generally flattened constructionhaving a pair of opposing faces and the head also has a transverse axislying orthogonal to the longitudinal axis and generally parallel to theopposed faces. References to transverse or longitudinal herein refer todirections which are respectively parallel to these transverse andlongitudinal axes, unless indicated otherwise.

An essential feature of the implement of this invention, and of theprocess for forming an implement is that the implement, or the implementthereby formed, includes a resiliently flexible joint in the handle orthe head, the joint comprising a plastic material and an elastomer. By“resiliently flexible joint” herein is meant a region comprising bothplastic material and elastomer which is able to articulate on theapplication of a force experienced under normal usage conditions for theimplement, and further, that when the force is removed the implementwill return to essentially the same starting configuration within 60seconds, preferably within 30 seconds. Preferably the head includes sucha resiliently flexible joint.

The head and handle are generally made of relatively non-compressiblematerials, preferably with a modulus of elasticity of at least about 500MPa, more preferably at least about 1000 MPa, which are conventional inthe manufacture of toothbrushes, especially plastic materials.Especially the plastic material has a Vicat softening point of less than245° C., more preferably less than 220° C. and especially less than 200°C. Suitable plastic materials include, for example, polyamides andpolypropylenes. Polypropylene is preferred. Suitable polypropylenesinclude the material ‘Polypropylene PM 1600’ (marketed by Shell), havinga modulus of elasticity (ISO 178) of 1500 MPa and Apryl 3400 Ma1 fromElf Atochem. Preferably, a foaming agent such as Hydrocerol HP20DP fromBoehringer-Mannheim is mixed with the polypropylene at a level of fromabout 1% to about 3%, preferably from about 1.5% to about 2.5%, byweight of the polypropylene. The foaming agent assists the flow of thepolypropylene during moulding and, in particular, helps to ensureuniform formation of hinges, where used. The handle itself is generallyrigid and may be of a shape which is conventional in the manufacture oftoothbrushes. Optionally, the handle may comprise a neck portion whichis more flexible than the rest of the handle, for example by inclusionof a flexible joint as described herein.

In a first step of the process according to the invention, an implementblank is provided which includes at least one region of plastic materialdefining a void space in the head or the handle. The implement blank isessentially the implement before injection of the elastomer and,optionally, before other finishing processes, such as attachment of thegrooming means. The at least one region of plastic material can be thewhole of the implement blank or some smaller portion of it. Suitableplastic materials are described hereinabove. The void space can be asimple groove in the head or a more complex shape. It should be ofdimensions such that the head or handle is weakened or otherwise madeflexible at that point. In preferred embodiments herein the implementblank includes one or more void spaces in the form of grooves or gapswhich divide the head into segments. Preferably there are two, three orfour segments, more preferably four. Many more than this increases themanufacturing complexity and, in a toothbrush where bristle tufts areinserted only into the head segments, makes it difficult to achieve asufficiently high tuft density on the brush head. The head segments canhave any suitable spatial relationship to each other such as being inlayers or arranged, for example, in quadrants of the brush head.Preferably, the segments are disposed in longitudinal sequence along thehead so that a longitudinal line drawn from the handle end of the headto the free end of the head passes through the first head segment thenthe second head segment and so on. More especially, there is a firsthead segment which is connected to or continuous with the handle and oneor more additional head segments arranged in longitudinal sequencetowards the free end of the head. Preferably also, the segments are amonolayer so that any line drawn through the head perpendicular to itstwo opposed faces will generally pass through only one sort of material.In general, each head segment will be made of the same material whichwill preferably be the same material as the handle so that they can allbe made in a single injection moulding step.

In the finished implement, all the head segments are connected by aconnecting means. The connecting means can take any form which issuitable for the implement in its intended function, provided that thereis at least one resiliently flexible joint where the elastomer is fusedto a plastic region. The connecting means can, for example, be adhesive,plastic links which are integral with or detachably connected to thehead segments, metal links, or elastomer which is fused to plasticsegments. In preferred embodiments herein, at least one of the segmentsis jointed to an adjacent segment or to the handle by a connecting meansconsisting essentially of an elastomer having a modulus of elasticity ofless than 500 MPa. By “consisting essentially of an elastomer” herein ismeant that the elastomer is the sole mechanical link between the onesegment and the adjacent segment or handle. By sole mechanical link,what is meant is that there are no continuous, non-elastomeric linkssuch as bridges or springs connecting the segments. The elastomer may,however, have other materials dispersed within it, such as flecks ofmetal or pigments which might be used, for example, to provide adistinctive appearance. These additional materials will generally make anegligible contribution to the mechanical connection between thesegments and/or handle such that their removal would not materiallyalter the strength of connection. In preferred embodiments there are oneor more segments which are unconnected until the elastomer is injected,and the implement blank may comprise several unconnected segments whichare held in position relative to each other only by the mould in whichthe implement blank is prepared and provided. The gaps between thesegments are void spaces which, if filled by elastomer, can constituteresiliently flexible joints, so that one segment can articulate relativeto another.

In highly preferred embodiments herein the head has a top face and abottom face and the connecting means consist of bands of elastomerextending transversely across the head and from the top face to thebottom face. For example, in a head comprising four segments,longitudinally sequenced along the head, with the first segment beingco-extensive with the handle, there are three such connecting means. Thebands of elastomer can vary in thickness, either from one band to thenext or even across the width or along the depth of the band. Suitably,their thickness, measured along the longitudinal axis, is in the rangefrom about 0.1 mm to about 10 mm, preferably from about 0.3 mm to about5 mm, more preferably from about 0.5 mm to about 3 mm.

In alternative embodiments the segments are additionally connected byhinges of the same material as the segments, the hinges being thinner ornarrower than segments they connect, and the whole implement blankforming one interconnected piece. There can of course, within the sameimplement, be some connecting means which comprise hinges and otherswhich consist essentially of an elastomer. The voids between thesegments connected by hinges will be referred to herein as grooves.

The grooves can be of variable width and depth and the distances betweengrooves can also be varied. In this manner the flexibility of the headalong the length and/or across the breadth of the head can be modified.Preferably only transverse grooves are varied in this way. Changing thedepth of the grooves controls the location and thickness of the hingeswhich connect the segments. In preferred hinged embodiments the head hasa pair of opposing faces with grooves on each face located opposite eachother in pairs so that there is a residual hinge between the two faces.For a toothbrush head of between about 4 to about 6 mm thickness,typically about 5 mm, suitable groove depths are in the range from about1.4 to about 3 mm, preferably from about 1.5 to about 2.8 mm. Suitablehinge thicknesses are in the range from about 0.4 to about 2.0 mm,preferably from about 0.5 to about 1.5 mm. Where transverse grooves areused then, desirably, the hinges which are or will be nearer to thehandle are less flexible than those which are or will be more remotefrom it. In this way more uniform bending of the head can be achieved.The variation in flexibility can be achieved by varying the hingethicknesses. In a preferred embodiment the hinge nearest the handle isup to about 3 times, preferably up to about 2 times as thick as thehinge most remote from the handle. An exemplary set of hinge thicknessesfor a toothbrush with 3 transverse grooves are respectively about 1.2,0.6 and 0.6 mm reading from the handle end. If identical hinges are usedalong the brush head then there is a tendency for flexing of the head tooccur predominantly at the hinge nearest the handle. The depth ofgrooves on one face can be different to those on the opposing face.

Increasing the width of the grooves increase the gap between thesegments and therefore the length of the hinges, which increases theirflexibility. However, since it is preferred for the grooming means, suchas bristles, to be supported on the segments rather than on elastomerinjected between the segments, increased groove length also leaves lessspace for the grooming means, within a given head size. Suitable groovewidths are in the range from about 0.3 to about 3.0 mm, preferably fromabout 1.2 to about 2.0 mm. The grooves are preferably tapered slightlyinwards towards the bottom of the groove, suitably converging at anangle of from about 3 to about 10°, to facilitate moulding. As theimplement is flexed the width of the groove changes, more rapidly at thetop of the groove than at the bottom of the groove, the relative changebeing a function of the groove width and depth. Since this change ingroove width results in compression or tension of elastomer containedwithin the groove, it can be seen that, for a given elastomer, thegroove geometry can be used to control the flexure of the implement.

The hinges can be the full length of the grooves or, preferably, therecan be one or more gaps in or to the side of the hinges the grooves inthese regions being the full depth of the head. This has the advantageof permitting a single injection point for the elastomer when mouldingthe head. The gap allows elastomer to flow from one face to the otherduring the moulding process. In a preferred embodiment, the hinges arediscontinuous, with two or more hinges, preferably just two, connectingeach segment to its neighbour or to the handle. In this embodiment thereare gaps between the hinges and to each side. In linear grooves, thehinge widths are not generally critical, provided that they are suchthat gaps are still created, however, wide hinges can be subject todistortion if they are used within a non-linear groove. Suitable hingewidths are in the range from about 0.5 to about 4.0 mm, preferably fromabout 1.0 to about 3.0 mm.

It is preferred that each hinge is located between the two faces and ata distance of at least about 10%, preferably at least about 20%, morepreferably at least about 30% of the depth of the head from each of thefaces. The distance of the hinge from the face is measured by theperpendicular line drawn from the top of the face to the nearestboundary surface of the centre of the hinge. Locating the hinges awayfrom the faces of the implement head means that they are subject to lessstretching or compression as the head is flexed and improves theirdurability. In a particularly preferred embodiment, the implement headhas transverse grooves which are arranged in pairs such that one memberof each pair is on each face and directly opposes the other member ofthe pair, with one or more hinges therebetween connecting the segmentsso that each hinge is located between the two faces and at a distance ofat least about 10%, preferably at least about 20%, more preferably atleast about 30% of the depth of the head from each of the faces.

In a second, essential step of the process according to the invention,elastomer is injected into the void space(s) at a temperature of atleast about 245° C., thereby fusing the elastomer to the plasticmaterial and forming the resiliently flexible joint. Preferably theelastomer is injected at a temperature in the range from about 245° . toabout 270° C., more preferably in the range from about 250° C. to about260° C. The injection temperature is the temperature at which theelastomer enters the mould. In a typical injection moulding setupinvolving a screw-feed injection cylinder this may not be the same asthe temperature of the elastomer in the cylinder. Preferably a lowertemperature is employed in the cylinder, of around 210° C. to about 220°C., to reduce the possibility of burning or thermal degradation of theelastomer, heating to the final injection temperature being provided viaa hot runner between the cylinder nozzle and the final injection point.

Other preferred conditions for the elastomer injection step include:

a) An injection pressure in the range of from about 30 to about 80 MPa,preferably from about 40 to about 70 MPa, more preferably from about 50to about 60 MPa and an elastomer injection time of less than one second,preferably less than about 0.8 s. Short injection times facilitate theelastomer reaching all the flexible joint areas at the desiredtemperature.

b) A holding pressure, after the elastomer has been fully injected, inthe range of from about 5 to about 15 MPa, preferably from about 8 toabout 12 MPa, held for between about 2 to about 5 seconds.

Elastomers are well known in the art of injection moulding. The term“elastomer” herein refers to a material which is both elasticallycompressible and elastically extensible. For the purposes of thisinvention, suitable elastomers have a modulus of elasticity of less than500 MPa. Preferred elastomers for use herein have a modulus ofelasticity of less than about 300 MPa, especially preferred arethermoplastic elastomers with a hardness of about 30 Shore A to 74 ShoreD, polyolefin types such as styrene-ethylene-butylene-styrene (SEBS) arepreferred, for example those based on Kraton® G, but other classes ofelastomer, such as polyurethanes and polyamides, can also be used. Anexemplary elastomer is ‘PTS Thermoflex 75’ (marketed by PlasticTechnologie Service, Germany), having a modulus of elasticity (ISO 178)of 100 MPa and a hardness (ISO 868) of 80 Shore A. Elastomers PL12291,PL12292, and PL12293 (marketed by Multibase, Saint Laurent Du Pont,France) are also suitable for use herein. In general, choosing theelastomer so that is based upon the same chemical class of polymers asmaterial of the head segments assists in fusing the elastomer to thehead segments. For example, when the head segments are made frompolypropylene, the elastomer is preferably based upon a polyolefin. Theelastomers can optionally be mixed with a suitable plasticiser orfoaming agent to make them more compressible. The colour of theelastomer material can be the same as that of the head segments, or itmay be different thereby achieving a distinctive striped or otherwisepatterned appearance. More than one type of elastomer can be used withinthe implement as a whole. This may be appropriate, for example when itis desired to modify the head flexibility progressively along itslengths. One way of achieving this is to use a soft elastomer as theconnecting means between the pair of segments closest to the free end ofthe head and a hard elastomer as the connecting means between the pairof segments closest to the handle end of the head.

The elastomer is preferably fused to the adjacent segments and/or to thehandle so that the elastomer can be stretched to about 120%, preferablyto about 150%, more preferably to about 200% of its unstressed lengthwithout separation of the elastomer from the head segments. This makesthe present invention particularly suitable for constructing flexiblehead toothbrushes as will be described further herein. The degree andextend of fusion is sufficient that the elastomer can be stretched to atleast abut 120% of its unstressed length without separation of theelastomer from the head segments and/or handle. Preferably at leastabout 50%, more preferably at least about 75%, especially about 100% ofthe interfacial area between the elastomer and the head segment orhandle, in any one elastomer/segment interface is fused in this way.

By “without separation of the elastomer from the head segments and/orhandle” herein is meant that the elastomer does not become completelydetached from the head segments and/or handle. Since even partial lossof attachment of the elastomer to the head segment or handle cancompromise the function and/or integrity of the implement, it ispreferred that even partial detachment is avoided. In preferredembodiments, the elastomer will become detached over less than about30%, preferably less than about 15%, more preferably less than about 5%of the fused interfacial area between elastomer and head segment orhandle when the elastomer is stretched to at least about 120%,preferably to about 150%, more preferably to about 200% of itsunstressed length. The above results should hold true whether theelastomer is stretched by linear deflection, bending or torsionalmovements of a segment relative to the adjacent segment or handle.Since, for some geometries of segment-segment or segment-handleconnections, or for bending or torsional movements of one segmentrelative to its neighbour, there will be varying extents of elastomerstretching across an interface, care is required in measuring partialdetachment. In such cases of differential elastomer extension, at eachpoint on any one interface to be measured, the stretching should bemeasured along a line drawn through the elastomer which is perpendicularto the interface at the point where separation is to be determined, whenthe implement is in its rest, unstressed state. In bending or torsionalmodes it may be that this line will deviate from the perpendicular asone segment is moved relative to the other.

Over its lifetime, an implement having a resiliently flexible head, asdescribed herein, may be subjected to stretching of the elastomer bye.g. bending of the head, many thousands of times. Preferably then, theelastomer-segment bond is able to withstand repeated extension andrelaxation of the elastomer, to the extent described above, and back tothe rest state through at least 10,000, preferably at least 25,000, morepreferably 75,000 extension-relaxation cycles.

In highly preferred embodiments herein the head comprises at least onelongitudinal groove which connects transversely disposed bands ofelastomer and permits the elastomer to flow from one band to the otherduring an injection moulding process. In an implement with a co-mouldedhandle, this longitudinal groove can extend along the handle so that thesame elastomer injection point in the mould that is customarily used forsupplying elastomer to form handle grips can also be used to inject theelastomer into the void spaces in the head. Normally this longitudinalgroove will not extend through the full depth of the handle or head atall points, though it can do so where desired, for instance to provideopposed grip points on top and bottom surfaces of the handle.

The present invention is particularly suitable for the manufacture ofimplements having a resiliently flexible head. By “resiliently flexiblehead” is meant herein that when a 3 Newton force is applied to one endof the head, the other end being held fixed, the end to which the forceis applied will deflect through an angle of at least 2° and, when the 3Newton force is removed, the head will return to its original positionwithout the application of external force. The end of the head which isto be held fixed is defined by the line which is perpendicular to theaxis along which bending takes place and which touches the first pointto comprise a grooming means, such as a row of toothbrush bristles. Theend of the head where the force is to be applied is the opposite end ofthe head at the furthest point away along the bending axis. The anglethrough which the head bends when a 3 Newton force is applied as aboveis referred to herein as the flex angle. The flex angle can convenientlybe measured by measuring the vertical displacement (y) of the free endof the head under a 3 Newton force and the distance y and the distancebetween the clamping point and the application of the force (x), theflex angle being derived by the relationship tan(flex angle)=y/x. Inpreferred embodiments the flex angle is at least 3°, more preferably atleast 5° and it can be as high as 15° or more.

In preferred embodiments herein, the implement comprises a groomingmeans on only one face of the head and that face is concavely shaped. Inthese embodiments the head preferably has a flex angle such that theconcave face is able to bend to the extent that the face can becomeconvex. In its rest state, the face of the head comprising the groomingmeans can be concave along either its longitudinal or transverse axis.Where the face is concave along the longitudinal axis, the radius ofcurvature may vary along the length of the head. The radius of curvatureis preferably from 10 to 500 mm, more preferably from 15 to 250 mm,especially from 25 to 150 mm.

In use, toothbrushes according to this invention can be used forcleaning the teeth by an entirely conventional tooth brushing handaction, preferably in a manner recommended by dental health authorities.The implement can also be an electrically driven toothbrush.

The invention will now be described by way of example only, withreference to the accompanying drawings in which:

FIG. 1 is a perspective view of a toothbrush according to the invention.Some of the bristles are omitted for the sake of clarity.

FIG. 2 is a partial side view of the head of a toothbrush according tothe invention.

FIG. 3 is a plan view of the bottom face of the head of a brushaccording to the invention.

FIG. 4 is a perspective view of a hinged toothbrush according to theinvention; the elastomer is not shown in order to show the hinges andgrooves more clearly.

FIG. 5 is a schematic showing the measurement of the flex angle.

Referring to FIG. 1, a toothbrush 1 has a resiliently flexible,flattened head 2, having a top face 3 and bottom face 4 which aresubstantially parallel to each other, and an elongated polypropylenehandle 5. The head comprises four polypropylene segments 6, the first ofwhich is continuous with handle 5. The segments are connected only bybands of a SEBS elastomer 7 having a hardness of 60 Shore A. Thesegments 6 are longitudinally sequenced along a longitudinal axis A—A.The bands of elastomer 7 extend across the transverse axis of the headB—B and from the top face 3 to the bottom face 4. Tufts of bristles 8extend from top face 3. In practice, the brush has bristles extendingfrom each of the four segments. Top face 3 is slightly concave, alongthe longitudinal axis A—A, having a radius of curvature of about 75 mm.The bands of elastomer afford sufficient flexibility to the brush headthat it can bend along the longitudinal axis until the top face becomesconvex. In doing so the elastomer is stretched along the top face. Theelastomer on this face can stretch to more than 200% of its unstressedlength without any observable loss of attachment of the elastomer to thesegments. The head is able to repeatedly flex to this extent and back tothe rest state through 75,000 cycles, without any detachment of theelastomer from the head segments. The handle comprises further regions 9of the same elastomer to form a functional and attractive grip. Thetoothbrush is made by sequential injection moulding of first thepolypropylene to form the handle 5 and segments 6 and then in a secondstep the elastomer is injected at a temperature of 255° C., therebybecoming fused to the polypropylene. After the brush has cooled thebristle tufts are inserted by the stapling technique into preformed tuftholes.

Referring to FIG. 2, a toothbrush head 2 having a free end 10 and handleend 11 is formed integrally at one end of a handle 5. The head includesfive segments 6 which are longitudinally sequenced along the head. Thesegments are flexibly connected by bands of elastomer 7 and the segmentnearest the handle end 11 is flexibly connected to the handle 5 only bya band of elastomer. The bands of elastomer 7 extend completely acrossthe transverse axis of the head and taper from the top to the bottomface. Along the top face the bands of elastomer have a width of about1.2 mm and along the bottom face the bands of elastomer have a width ofabout 0.8 mm. Tufts of bristles 8 extend from the top face of the head.The toothbrush is made by sequential injection moulding and subsequenttufting as described above.

Referring to FIG. 3, a toothbrush head 2 is formed integrally at one endof a handle 5. The head includes four segments 6, one of which iscontinuous with handle 5. The segments are connected only by bands of aSEBS elastomer 7 having a hardness of 60 Shore A and which have a waveprofile across the transverse axis of the head. A longitudinal groove 12extends along the bottom face of the head and the handle, connecting thebands of elastomer so that they can all be formed from a singleelastomer injection point.

Referring to FIG. 4, a toothbrush 1 has a head 2 which is co-mouldedwith the handle 5, the head being concave along its longitudinal axis onthe top face 3. Voids 13 in the handle are filled with elastomer toprovide hand grips. The voids are connected to each other by alongitudinal groove 12 on the bottom side of the handle which extendsinto the head and connects transverse grooves 14 between segments 6. Thesegments are connected by thin hinges 15. The elastomer in the voids andthe grooves can be injected from a single injection point 16 and is of adifferent colour to the head material to give a distinctive appearance.The head has holes 17 disposed on the top surface thereof to accommodatetufts of bristles.

FIG. 5 illustrates the measurement of the flex angle. The head 2 isclamped 18 against the first row of bristles 19 at the end which isattached to the handle 5 and a 3 Newton force (F) is applied to theopposite end. The dashed lines show the original position of the brushhead before the force is applied. The vertical displacement (y) of thefree end of the head under the force F is measured and the flex angle isderived from the distance y and the distance between the clamping pointand the application of the force (x) by the relationship tan(flexangle)=y/x.

What is claimed is:
 1. A process for forming a grooming implement,comprising the steps of: i) providing a blank comprising a plasticmaterial and having a head and a handle, wherein said head has one ormore void spaces which divide said head into at least two segments; ii)injecting an elastomer having a modulus of elasticity of less than 500MPa into said void space at a final injection point at a temperature ofat least about 245° C. thereby fusing said elastomer to said segmentsand forming a resiliently flexible joint, wherein said elastomer is thesole mechanical link between said segments such that said segments canflex relative to each other; and iii) where said elastomer can bestretched to at least about 120% of its unstressed length withoutseparation of said elastomer from said segments.
 2. The process of claim1, wherein the grooming implement is a toothbrush.
 3. The process ofclaim 1, wherein said elastomer can be stretched to about 150% of itsunstressed length without separation of said elastomer from saidsegments.
 4. The process of claim 1, wherein said elastomer can bestretched to about 200% of its unstressed length without separation ofsaid elastomer from said segments.
 5. The process of claim 1, whereinsaid elastomer is injected at temperature between about 245° C. andabout 270° C.
 6. The process of claim 1, wherein said elastomer is apolyolefin.
 7. The process of claim 6, wherein said polyolefin is astyrene-ethylene-butylene-styrene elastomer.
 8. The process of claim 1,wherein said at least two segments are formed from polypropylene.
 9. Theprocess of claim 1, wherein said head comprises two bands of saidelastomer.
 10. The process of claim 1, wherein said elastomer forms anon-linear band.
 11. The process of claim 1, wherein said elastomerforms a band and wherein the interfacial walls of said band aresubstantially perpendicular to a face of said head.
 12. The process ofclaim 11, wherein said face is a top face.
 13. The process of claim 1,wherein said elastomer detaches over less than about 5% of the connectedinterfacial area between said elastomer and said segments when saidelastomer is stretched to at least about 120% of its unstressed length.14. The process of claim 1, wherein said elastomer is injected by aninjection molding apparatus having a cylinder and a cylinder nozzle andthe temperature in said cylinder is between about 210° C. and about 220°C.
 15. The process of claim 14, wherein said injection molding apparatusfurther comprises a hot runner disposed between said cylinder nozzle andsaid final injection point, wherein said elastomer is heated to saidtemperature of at least about 245° C. by said hot runner.
 16. A processfor forming a toothbrush, comprising the steps of: i) providing a blankcomprising a plastic material and having a head and a handle, whereinsaid head has one or more void spaces which divide said head into atleast two segments; ii) injecting an elastomer having a modulus ofelasticity of less than 500 MPa into said void space at a finalinjection point at a temperature of at least about 245° C. therebyfusing said elastomer to said segments and forming a resilientlyflexible joint, wherein said elastomer is the sole mechanical linkbetween said segments such that said segments can flex relative to eachother; and iii) wherein said elastomer can be stretched to at leastabout 120% of its unstressed length without separation of said elastomerfrom said segments and wherein said elastomer detaches over less thanabout 5% of the connected interfacial area between said elastomer andsaid segments when said elastomer is stretched to said at least about120% of its unstressed length.
 17. The process of claim 16, wherein saidelastomer can be stretched to about 150% of its unstressed lengthwithout separation of said elastomer from said segments.
 18. The processof claim 1, wherein said elastomer can be stretched to about 200% of itsunstressed length without separation of said elastomer from saidsegments.
 19. The process of claim 1, wherein said elastomer is injectedat temperature between about 245° C. and about 270° C.
 20. The processof claim 19, wherein said elastomer is a polyolefin.
 21. The process ofclaim 1, wherein said elastomer forms a band and wherein the interfacialwalls of said band are substantially perpendicular to a face of saidhead.
 22. The process of claim 21, wherein said face is a top face. 23.The process of claim 16, wherein said elastomer is injected by aninjection molding apparatus having a cylinder and a cylinder nozzle andthe temperature in said cylinder is between about 210° C. and about 220°C.
 24. The process of claim 23, wherein said injection molding apparatusfurther comprises a hot runner disposed between said cylinder nozzle andsaid final injection point, wherein said elastomer is heated to saidtemperature of at least about 245° C. by said hot runner.
 25. Theprocess of claim 1, wherein said elastomer can be stretched to said 120%of its unstressed length for at least 10,000 extension-relaxation cycleswithout separation of said elastomer from said segments.
 26. The processof claim 25, wherein said elastomer can be stretched to 200% of itsunstressed length for at least 25,000 extension-relaxation cycleswithout separation of said elastomer from said segments.
 27. The processof claim 16, wherein said elastomer can be stretched to said 120% of itsunstressed length for at least 10,000 extension-relaxation cycleswithout separation of said elastomer from said segments.
 28. The processof claim 27, wherein said elastomer can be stretched to 200% of itsunstressed length for at least 25,000 extension-relaxation cycleswithout separation of said elastomer from said segments.